WHO aside, presumably he did believe that they knew that these treatments lacked scientific support. What seems to be being demonstrated is that chiropractic organizations in general are quite aware of this and are uncomfortable about defending these (non-lower back related) treatments in court.
My understanding was that if they believed that, despite the fact that the evidence for these treatments was not in their favour, these treatments worked, then they didn't believe they were 'bogus'. If the treatments are bogus, but the chiropractors don't/won't believe it then Simon Singh was still in error to say that they were happily promoting bogus treatments.
If the current official interpretation of his comments stand, he is sunk. Hopefully there is a book in it for him.
By the way, how come homeopaths get to claim they can treat all sorts of bogus stuff, by chiropractors get taken to the ASA if they do the same?